The Hazards of the Salmon Farming Industry

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The Hazards of the Salmon " Farming " Industry

 

 

The Hazards of the Salmon " Farming " Industry

 

 

Drugs used in the salmon farming industry

 

A variety of chemicals, including antibiotics, pesticides and

 

fungicides are used on salmon farms to treat disease outbreaks.

 

These drugs are often administered to the fish through their feed.

 

Since salmon are mostly raised in open marine netcages, most of the

 

drug, or its metabolic byproducts, end up in the marine environment

 

through uneaten feed or the salmon's excrements (1). The

 

distribution and environmental impact of these chemicals is a cause

 

of great concern.

 

Antibiotics

 

 

The most common antibiotic used is oxytetracycline, with 6.4 metric

 

tonnes used on B.C. salmon farms in 1998 (2). Others include

 

fluorfenicol and a class known as sulfonamides. It has been shown

 

that oxytetracycline is poorly absorbed by the intestinal tract of

 

the salmon (3). Consequently much of the drug is excreted unchanged

 

into the marine environment, where it distributes itself between the

 

sediment and water column, or is ingested by wild sealife (4).

 

Studies show that some antibiotics, including oxytetracycline and

 

fluorfenicol, persist in the environment, and marine sediment acts

 

as a long-term reservoir for them (5).

 

 

Not surprisingly, investigators have shown that antibiotics can

 

significantly alter the microbial community found in marine

 

sediment. Not only can the total amount of bacteria be reduced, but

 

also the relative abundance among the different species is altered.

 

Sediment-dwelling bacteria provide a number of key services, in

 

particular the cycling of nutrients such as nitrogen, phosphorous

 

and sulfur. Measurements reveal that antibiotics found in marine

 

sediment near salmon farms lower the conversion rates for sulphates

 

and nitrates.

 

 

What consequences may arise from an altered marine microbial

 

community has not been studied. There is also the question of the

 

possible effects of any chemicals produced when the fish

 

metabolically convert the administered antibiotic. For example, when

 

salmon ingest florfenicol, the fish converts some of the antibiotic

 

to florfenicol amine. There are no studies on how this, or other

 

antibiotic metabolites, can affect the natural marine community.

 

 

One area that has received a great deal of study, is the increase in

 

antibiotic-resistant bacteria in sediment under fish farms, in

 

farmed salmon, and in wild organisms caught near salmon farms. The

 

implications that this has for human health is covered in some of

 

our other information sheets. With respect to the marine

 

environment, however, it should be mentioned that increases in

 

antibiotic-resistant bacteria leads to increased use of antibiotics

 

on the salmon farm, increasing the environmental risks.

 

 

Pesticides

 

 

Sea lice infestations often cause problems at salmon farms, and are

 

the primary reason that pesticides are used. The fish are treated

 

with these chemicals in one of two ways. One is by using a tarpaulin

 

to isolate the fish within the netcage and then adding the chemical

 

in the seawater. After 30-60 minutes, the tarpaulin is removed and

 

the solution is released to the marine environment (6). This method

 

is used for pesticides such as cypremethrin , dichlorvos and

 

azamethiphos. Other pesticides, such as ivermectin, are administered

 

within the feed.

 

 

The Canadian Pest Management Regulatory Agency has only approved

 

azamethiphos for use against sea lice. Although not approved, the

 

other pesticides are used with the permission of a veterinarian,

 

often with little or no data available on their effects on the

 

marine environment.

 

 

Sealice and Ivermectin

 

 

In BC, sealice are often treated using ivermectin. A high proportion

 

of the administered chemical is excreted unchanged by the salmon,

 

and accumulates in marine sediment beneath and in the vicinity of

 

the fish farm. It can take 90 - 240 days for just half of the

 

chemical in the sediment to decompose. Recent analysis of sediment

 

under salmon farms has shown levels of ivermectin up to 6.8

 

milligrams (mg) per kilogram of sediment. This concentration went

 

down with distance from the farm, but in some samples still showed a

 

concentration of 5.4 mg per kg of sediment 35 metres from the

 

netcage. The accumulation of ivermectin was also expressed as amount

 

per unit area. This gave figures of .675 mg per square metre (m-2)

 

for under the cage and .357 mg m-2 for the sample at 35 metres from

 

the netcage.

 

 

Ivermectin has the ability to disrupt neurological processes. It

 

also can bind to biological membranes, increasing their permeability

 

to chloride ions (a main component of sea water) (7). It therefore

 

has the potential to be toxic to a wide variety of marine organisms.

 

To date studies have shown the chemical to be very toxic to many

 

species that live in or on the seabed.

 

 

 

Table 1: Studies which show lethal effects of ivermectin on various

 

marine organisms

 

Asterias rubens(a starfish)(7) 5 mg/kg

 

Corophium Íolutator ( sediment worm)(7) 0.05 mg/kg</td>

 

Crangon septemspinosa (a shrimp)(8) 8.5 micrograms per gram of feed

 

shrimp has access to.

 

Arenicola marina (a marine worm)(9) 0.018mg/kg

 

8 species of polychaetes (a class of marine worms)(10) 8 - 80 mg/

 

sq. metre depending on species.

 

 

Table 1 lists some of the species that have been tested and the

 

concentrations of ivermectin for which the species begins to die

 

off. It can be seen that the concentrations that are lethal to these

 

organisms are in the range of what has been measured under and near

 

salmon farms (see paragraph above).

 

 

The lethal effect of ivermectin on the polychaetes is particularly

 

interesting. This large class of marine worms is often a crucial

 

part of many marine food chains. They also are key to the

 

decomposition of accumulated organic matter, such as fish feces and

 

uneaten feed that accumulates under salmon farms. The worms

 

constantly turn over the marine sediment allowing oxygenated water

 

to reach aerobic decomposing bacteria. Without these worms, the

 

marine sediment can become depleted in oxygen and proper

 

decomposition cannot occur.

 

 

Two of the other pesticides, cypermethrin and azamethiphos, used on

 

salmon farms have also been shown to have toxic effects on marine

 

organisms. A recent study showed that cypermethrin is lethal to

 

lobster larvae at concentrations of 0.06 to 0.16 micrograms per

 

litre of seawater (11). The same study showed that azamethiphos

 

killed shrimp and adult lobster at concentrations of 50 micrograms

 

per litre of seawater. Sub-lethal concentrations of azamethiphos at

 

5 and 10 micrograms per litre were also shown to reduce spawning in

 

female lobster.

 

 

The use of pesticides on salmon farms results in negative impacts on

 

marine organisms found near the salmon farm. The effect on many more

 

marine organisms needs to be studies, as well as the effects of sub-

 

lethal concentrations, which has received very little attention.

 

 

 

References

 

1. Lunestad, B.T., 1992. Fate and effects of antibacterial agents in

 

aquatic environments. In: Michel, C.M., Alderman, D.J. Eds. ,

 

Chemotherapy in Aquaculture: From Theory to Reality. Office

 

Internationale des Epizooties, Paris, pp. 151-161.

 

 

2. Paone, S. Farmed and Dangerous:Human Health Risks Associated With

 

Salmon Farming. A Report Prepared for Friends of Cloyoquot Sound,

 

November, 2000

 

 

3. Samuelsen, 1994.

 

 

4. GESAMP 1997.

 

 

5. Samuelsen, 1994

 

 

6. Haya, K., et. al., Environmental impacts of chemical wastes

 

produced by the salmon aquaculture industry. ICES Journal of Marine

 

Science, 58, 492-496, 2001.

 

 

7. Davies, I.M., et. al., Environmental risk of ivermectin to

 

sediment dwelling organisms. Aquaculture, 163: 29-46, 1998.

 

 

8. Davies, I.M., A review of the use of ivermectin as a treatment

 

for sea lice [Lepeophtheirus salmonis (Kroyer) and Caligus elongatus

 

Nordmann] infestation in farmed Atlantic salmon (Salmo salar L.).

 

Aquaculture Research, 31: 869 - 883, 2000.

 

 

9. Thain, J., et. al. Acute Toxicity of ivermectin to the lugworm

 

Arenicola marina. Aquaculture, 159: 47-52, 1997.

 

 

10. Collier, L. An assessment of the acute impact of the sea lice

 

treatment ivermectin on a benthic community. Journal of Experimental

 

Marine Biology and Ecology, 230: 131-147, 1998.

 

 

11. Haya, K., et. al. Environmental impact of chemical wastes

 

produced by the salmon aquaculture industry. ICES Journal of Marine

 

Science, Vol. 58: pp. 492-496, 2001.

 

 

http://www.davidsuzuki.org/Oceans/Fish_Farming/Salmon/Drugs.asp